Heating and cooling of air for ventilating, warming and refrigerating purposes



Aug. 3, 1965 c. E. OVER 3,197,969

HEATING AND COOLING OF AIR FOR VENTILATING, WARMING AND REFRIGERATINGPURPOSES Filed Feb. 24, 1964 4 SheetsSheet 1 N VENTOR @4144. M 161w;@hvW A TTORNEVJ' 3,197,969 TI ING, WARMING PO Aug. 3, 1965 c. E. OVERHEATING AND COOLING OF AIR FOR VEN AND REFRIGERATING PUR 4 Sheets-Sheet2 Filed Feb. 24, 1964 Aug. 3, 1965 c. E OVER HEATING AND COOLING OF 4AND REFRIGERATING PURPOSES Filed Feb. 24, 1964 AIR FOR VENTILATING,WARMING 4 Sheets$heet 3 A Trek/v1.

Aug. 3, 1965 c. E. OVER 3,197,969

HEATING AND COOLING OF AIR FOR VENTILATING, WARMING AND REFRIGERATINGPURPOSES Filed Feb. 24, 1964 4 Sheets-Sheet 4 fes "r R? 76 -85 Q9 82 75ii 2 II Q; n ,1 r 22; :RQI'AQIAIF W} T \86 ET I: 74 -78 INVENTORATTORNEYS United States Patent HEATING AND COQLING @ll AIR FUR VENTILAT-TPITg,SWARMENG AND REFRTGERATING PUR- E Charles Edward Over, Eetchworth,England, assignor to Kinematics Limited, London, England, a Britishcompany Filed Feb. 24, 1964, Ser. No. 346,722 13 Claims. (Cl. 62-5) Thepresent invention relates to improvements in and relating to the heatingand cooling of air for ventilating, warming and refrigerating purposes,and is concerned with air heating and cooling apparatus of the in whichair is used as the working fluid.

Space-cooling refrigerators using air as the working fluid have beenknown for more than a century, but they have become obsolete due totheir bulk, complication and thermodynamically inferior performance ascompared with vapour compression refrigerators.

Nevertheless, an apparatus in which air is used as the working iluid hascertain important advantages. For example, air is a chemically safeworking fluid and costs nothing and there is no need in such anapparatus to have any moving parts other than a fan or compressor.

The operation of the present invention depends upon a phenomenon whichhas been observed in connection with inward radial flow turbines, namelythat the temperature of the air in the center of a centrifugal field isless than that at the periphery thereof.

It is believed that the cause of this phenomenon may be described ingeneral terms as follows:

If a stream of air (or other gas) is injected tangentially into acyclone or volute, a centrifugal field or vortex will be establishedwithin the casing. The layer of air at the periphery will be retarded byfriction with the walls of the casing. These molecules of air, beingsubject to the rules of centrifugal fields, will tend to move towardsthe center of the vortex.

The fast-moving molecules just inside the peripheral layer transfer someof their energy to this layer by bombarding some of its slower-movingmolecules and speeding them up. The net result of this process is theaccumulation of slow-moving low-energy particles at the center of thecyclone or volute and of fast-moving highenergy particles at theperiphery.

in the thermodynamics of gases, the terms highenergy and high-velocitydenote high temperature and low-energ and slow-moving denote lowtemperature. Consequently, there exists in such a cyclone or volute, arotating core of relatively cold air surrounded by a rotating belt orrim of relatively hot air.

The references in the preceding paragraph to hot air and cool air are tobe intepreted as referring to heating or cooling of the air by as littleas 1 or 2 F. or as much as 100 F., depending upon the choiceofdimensions and pressure variables in the apparatus under consideration.

In the improved apparatus according to this invention at least onecompressor or blower is arranged to discharge air in a substantiallytangential direction into a volute chamber containing a ring of guidevanes arrangedrto deilect air from the vortex formed in thecircumferential re gion of the volute chamber into a central regionthereof within the guide vane ring, a cold air outlet opening ofconsiderably smaller diameter than the inner diameter of the guide vanering is formed centrally in one end wall of the volute chamber and awarm air outlet opening of substantially the same diameter as the innerdiameter of the guide vane ring is formed centrally in the other endwall of the volute chamber.

Preferably two compressors or blowers are arranged to Patented Aug. 3,1965 deliver compressed air into the volute chamber through tangentialinlets on opposite sides respectively of its circumference. The greaterthe temperature difference required between the air discharged throughthe cold air and warm air outlet openings and the ambient temperature,the higher must be the pressure of the air delivered to the volutechamber by the compressors or blowers. For. a high pressure difference,up to a limit of lb. per square inch, it will be necessary to usereciprocating compressors, rotary sliding-vane blowers or 'Rootesblowers. Where, however, a large volumetric flow is required with asmaller temperature difierence, centrifugal compressors or fan typeblowers delivering air at pressures of, for example, from 2 to 10 lb.per square inch may be used.

The air under pressure from the or each compressor or blower isadvantageously passed through a heat exchanger before entering thevolute chamber, whereby the heat of compression is removed from it,either by water cooling or by fan cooling.

The guide vanes of the guide vane ring are preferably inclined so thatthe air passing between them is given a tangential component of motionrelative to the inside circumference of the guide vane ring. Thus, forexample, the angle between the air stream discharged from between anytwo adjoining guide vanes and a corresponding tangent to the insidecircumference of the guide vane ring is preferably less than 20.Consequently, a rotating vortex of air is formed within the guide vanering.

In large installations, the guide vanes may be pivolally adjustableabout their inner edges by means of a common control member, so thattheir angle of inclination can be varied simultaneously to suit variousdiiferent working conditions.

The warm air outlet opening preferably opens into the inlet end of awarm air outlet pipe, the length of which is advantageously 25 to 30times greater than the inner diameter of the guide vane ring. The boreof this warm air outlet pipe may, at its inlet end, be of the samediameter as the warm air outlet opening and the walls of this bore maytaper outwardly in the direction towards its outlet end at an includedangle of 5 to 8.

The warm air outlet pipe may be water-cooled, for which purpose it maybe surrounded by a water jacket with a helical. partition to cause thecooling water to flow helically around the pipe from one end thereof tothe other.

An adjustable throttling device is advantageously provided at the outletend of the warm air outlet pipe, so that a variable back pressure can beimposed on the warm or hot air discharge. In small installations, thiscan be a sluice or butterfly valve, but in larger installations itshould take the form of a variable aperture of the spear type whichgives an annular orifice at the periphery of the outlet pipe.

The cold air outlet opening may also be fitted with an outlet pipe orduct. The most suitable diameter for this opening in relation to thediameter of the guide vane ring will vary widely, depending upon theinlet air pressure and other operating variables. In largeinstallations, the diameter of this opening may therefore be madeadjustable, e.g. by using an adjustable iris diaphragm.

As a general and approximate guide, it is found that the coldest airtemperature is obtained when the fraction of cold air is about one thirdof the total quantity of inlet air, but appreciable and useful coolingeffects are obtained with considerably higher proportions of cold air tohot air. This variation in the ratio of hot air to cold air is producedby altering the back pressure in the hot air outlet pipe and also thesize of the aperture of the cold air outlet.

The variable apertures specified above enable these proportions of coldair to hot or warm air to be varied to suit the prevailing ambientconditions. For example, if the apparatus is used for ventilating andair conditioning, a greater cold air discharge will be required in hotweather than in cooler weather, which will also necessitate additionalblower power to augment the inlet air quantity, since to obtain agreater quantity of cold air at the cold end more hot air must bedischarged at the hot end.

The air cooling and warming apparatus according to this invention may beutilized in ventilating and air conditioning installations. For thispurpose, it may be located either outside or inside the space to beair-conditioned, but the air supply for the or each air compressor orblower is taken from outside this space. Thermostats situated in thespace to be air conditioned are linked with suitable actuating devicesin a temperature-responsive manner, to operate the throttle at the hotdischarge end and possibly the variable orifice at the cold dischargeend, in order to maintain the required temperature in the space.

In very hot weather, one or more additional compressors or blowers maybe switched in to discharge into the vortex chamber for feeding throughthe guide vane ring, to compensate for the reduction in volume of coldair which would otherwise be produced by the necessity of diminishingthe cold fraction to reduce its temperature. To accommodate thisadditional volumetric flow of inlet air, provision may be made foropening additional nozzle passages leading to the volute chamber.

In cold weather, on the other hand, when ventilation has to be combinedwith warming, means, including return ducts and flap valves, can beprovided for discharging the hot air discharge into the space and thecold air discharge into the atmosphere. Since, at the optimum setting,the fraction of hot air discharged is about two thirds of the inlet air,the apparatus performs more efiiciently under these conditions than as acooler.

There are many other applications particularly suited to this apparatusin which one space requires to be cooled and another adjacent spacesimultaneously requires to be heated. In many industrial processes it isrequired to pro duce a heating effect in one part of the process and asimultaneously cooling effect in another part of the same process. Bypassing the hot and cold air discharges through separate heat exchangersthis simultaneous heating and cooling can be achieved, thereby enablingthe apparatus to be run at maximum efliciency.

The air cooling and warming apparatus according to this invention canalso be employed for refrigeration purposes.

In domestic refrigerators and cold and cool rooms it is desirable toavoid direct contact between the air from the apparatus and the contentsof the cold chamber, since the air from the apparatus will have passedthrough the compressors or blowers and may be contaminated with oil oratmospheric impurities.

The cold chamber, therefore, is preferably provided with an inner metallining, leaving a circulation space around the outside of the liningbetween it and the inner wall of the chamber, which may vary from abouthalf-aninch in a domestic refrigerator to several inches in a cold room.One or both sides of the metal lining may be provided with extendedsurface fins to augment the heat transfer area. The inner chamber may,for cold and cool rooms, be provided with one or more circulating fans,so that the air in the inner chamber may be circulated against the innersurface of the metal lining to ensure maximum heat transfer for the airto the metal lining.

The air cooling apparatus is advantageously arranged so that the colddischarge is directed into the circulation space between the chamberwalls and the inner lining, at the bottom. For a small chamber ordomestic refrigerator, one cold air appaartus will be sufficient; forlarger cold chambers more than one apparatus may be arranged todischarge into the bottom of the circulation space at the circulationspace.

equidistant discharge points. The outer walls of the chamher areinsulated in the usual manner.

The cold air blown into the bottom of the circulation space displacesthe warmer air situated there initially. The warmer air is allowed toescape from one or more points at the top of the circulation spacethrough flap valves or lightly spring-loaded vents. The cold air may becaused to circulate in the space between the chamber walls and the innerlining by suitably disposed splitters or dividing plates, to cause thecold air to pass over the entire surface of the inner lining.

The sealed air in the inner chamber then gives up its heat, through themetal inner lining, to the cooler air in Hence as cold air is dischargedfrom the apparatus into the bottom of the circulation space, an equalmass of warm air is discharged through the vents at the top of thecirculation space.

One or more temperature-sensitive devices or thermostats have theirsensing elements situated in the inner chamber. When the temperature inthis chamber reaches the required lower value, the thermostat actuates acutout switch or other mechanism which stops the compressor or blowersupplying air to the apparatus, or otherwise diverts the inlet airsupply to the vortex chamber or opens a vent valve in the cold airsupply pipe. Alternatively, the thermostatic control is arranged toregulate the variable apertures so as to reduce the cold air input to alevel just suflicient to balance the heat leakage into the chamber.

The following is a practical example of the application of the presentinvention to a 12 cubic foot capacity domestic type refrigerator with anair supply at lb. per sq. inch. This air was supplied to the vortexchamber of the apparatus through /8 diameter tangential nozzle. The hotand cold air pipes were /2 diameter and the cold air escaped from thevortex chamber through a diameter opening, the throttle on the hot pipebeing approximately 'Vsths shut. The cold air was discharged into a /2wide circulating space between the metal inner lining and the chamberwalls and allowed to escape from a /2 diameter flap valve at the top.Under these conditions, the chamber was cooled from 60 F. to 25 F. in 60minutes.

The hot air discharge may be vented to atmosphere, but is preferablyutilized for heating purposes. For example, in the case of a domestictype refrigerator, the hot air discharge may be used to heat an airingcupboard or to heat water. To obtain hot air temperatures suitable forheating water, the air supply to the vortex chamber will be of the orderof 70 to lb. per sq. inch, in which case temperatures of over 100 F. canbe expected. In the case of high pressure air supply where the hot airis vented to atmosphere, a silencing device may be fitted to reduce thenoise level.

In such refrigerating applications as those described above, thecirculation space and the inner chamber may gradually become choked withfrost and ice. Defrosting is accomplished with this apparatus by aseries of flap valves, or other type of diverting device, whereby thecold air is shut off from the cold chamber and the hot air discharge, ora fraction of it, is directed into the circulation space. The hot airflow melts the frost and ice and the resulting water is removed througha drain valve or valves fitted at the bottom of the circulating spaceand inner chamber.

The invention will now be described by way of example with reference tothe accompanying drawings, in which:

FIG. 1 is a longitudinal section through an apparatus for cooling andwarming air,

FIG. 2 is a cross-section on the line IIII in FIG. 1,

FIG. 3 is a cross-section through a small domestic refrigerator orindustrial cooling cabinet,

FIG. 4 is a diagram illustrating a large scale installation for coolingand heating adjacent chambers.

Referring more particularly to FIG. 2, air is compressed by two rotarycompressors 1 and is passed by pipes or ducting, through heat exchangers2, in which the heat of compression is removed from it.

Leaving the heat exchangers 2, the air passes through buttterfly valves3 and is then discharged into a volute 4. Although two compressors areshown discharging into the volute 4 in FIG. 1, any number of compressorsfrom one upwards may be employed as the duty warrants. These compressorsare capable of being started or stopped, or of having their speedsregulated separately.

The volute contains a ring of guide vanes 5 pivoted at their inner endsto end plates 6. The outer parts of the guide vanes 5 pass through slotsin a ring 7, which can be caused to rotate by a link and screw mechanism8, operated by a hand-wheel 9. When the hand-wheel 9 is rotated, thelink 8 causes the ring 7 to rotate through a small arc and and the guidevanes 5, pivoting about their inner parts, with their outer edgessliding through the slots in the ring 7, are caused to alter their anglewith respect to a tangent to the inside circumference of the vane ring.Consequently, the area and angle of incidence of the guide vanes can bealtered.

In FIG. 1, a divergent pipe 15 is attached to one end of the vortexchamber 4, the angle of divergence being about 3 /2 degrees. The lengthof the divergent portion of the pipe 10 may be 25 to 30 times the theinner diameter of the guide vane ring. A water jacket 11 is fitted overthe divergent pipe lit, forming water-tight joints with it at each end.In FIG. 1, these Water-tight joints are formed by O ring seals 12 and13. Inlet and outlet pipes 14 and 15 are fittted to the water jacket 11.A helical strip 16 may with advantage be wound around between thedivergent pipe Ill and the water jacket 11. to ensure that the watereffectively cools the outer surface of the divergent tube It).

At the outer end of the divergent tube 10 is a spider having a centralboss 17 into which a stud 18 is screwed. A cone 19 can be screwed alongthe stud 18 so that the annular area between the cone and the end of thetube can be varied in order to give a greater or smaller throttlingeffect on the warm air leaving the tube.

In FIG. 1, on the other end of the vortex chamber is bolted a parallelpipe or duct 20. The diameter of this duct is less than that ofthe innerdiameter of the guide vane ring, but may vary between wide limitsdepending upon the air supply pressure and other operatingcharacteristics of the particular system involved.

To allow for the alteration of this effective diameter, an adjustableaperture 21 of the iris type is fitted to the duct adjacent to the'vortex chamber 4. This adjustable aperture, which is preferably ofcircular or near-circular shape, can be adjusted in diameter by anoperating lever 22.

An example of such a small apparatus will now be described withreference to FIG. 3.

In FIG. 3, an insulated container is constructed from an outer skin 31and an inner skin 32 between which is sandwiched a thermal insulatingmaterial 33. A lid 34 of similar sandwich construction is attached tothe top of the container by screwed fastenings 35.

Inside the inner skin 32 of the insulated container is an inner lining36 of thin sheet metal, supported by blocks 37 so as to leave acirculating space 38 between the inner lining 36 and the inner skin 32.A series of baffles 39 attached to the inner lining 36 subdivide thecirculating space 38 so as to form a labyrinth passage for cold air fromthe bottom to the top thereof. At the top of one side wall of thecontainer is a non-return flap valve 40, opening outwards, through whichair from the circulating space, under slight pressure, can escape to theatmosphere.

The insulated container is supported on a stand 41, provided with asound-absorbing lining 42, to bring the container to a convenientheight. A cooling apparatus 43, with its water jacket, is attached tothe stand so that its cold air discharge pipe 44 passes through thesandwich construction wall of the container into the bottom of thecirculating space 38.

Cooled air under pressure is supplied through an inlet pipe 45 to avortex chamber 46, which may have a single tangential nozzle and fixeddiameter orifices. The cold air generated in the vortex chamber passesinto the circulating space 33 through the pipe 4-4 and circulatesupwards around the bafiles 39 and out of the non-return flap valve iii.The warmed air from the vortex chamber passes downward through the waterjacket, which has inlet and outlet cooling-water connections 4-7 and 48,to a throttling valve 49 which may be a conventional gate or sluicevalve, having a handwheel 5% which can be adjusted from outside thecasing. The hot air outlet is led through a right-angled bend into asilencer 51 which may be of the conventional motor vehicle type and isfinally discharged to atmosphere through an exhaust pipe 52.

It is assumed that, in this example, there is no use for the warmexhaust air. As described above this could have been passed through aheat exchanger instead of the exhaust silencer 51 and could have heatedwater or performed other heating duty. If required, arrangements can bemade to return this hot air to the circulating space 33, through asystem of shut-off valves, for defrosting pur poses.

A dial thermometer 53 is fitted to any convenient part of the container,with its bulb 54 inside the container, to register the temperaturetherein. Alternatively, this temperature-sensitive element could be usedto shut oil the air supply when the required low temperature isattained.

In the large-scale installation illustrated in FIG. 4, the walls of acold chamber are constructed conventionally with an outer skin 61, anintermediate layer of insulation 62 and an inner skin 63. An innerlining 64 is arranged within the inner skin 63 so as to provide acirculation space 65. The inner lining 64 is of thin sheet metal havingbaliies 66 attached to it in the circulation space which define acirculatory path for the air passing from the bottom of this space tothe top. A fan 67 situated in the inner cold chamber 68 is driven by amotor 69 to circulate the air in the inner chamber against the innersurface of the metallic lining 64. At the bottom of the circulationspace are water drains 7t) fitted with shut-elf valves.

Cold air is discharged into the bottom of the circulation space 65through a duct 71 and passes upwards through the circulation space 65through passages defined by the divisions 66 and is discharged toatmosphere at slight positive pressure through a non-return fiap valve72.

The cold air is generated by apparatus similar to that described withreference to FIGS. 1 and 2, consisting of the cold air discharge pipe71, a volute 73, a Warm air discharge pipe 74 with a water-jacket 75 andcooling water inlet and outlet pipes 76 and 77 and a throttling device78. The warm air discharge pipe '74 discharges into a warm room 79 andleaves it through a non-return flap valve 83'.

Air is compressed in two compressors 81, and passes through heatexchangers 82, in which the heat of compression is removed and thenenters the volute 73. Thermostats 83 are located in the inner chamberand operate in one case an electrical actuator 84 which adjusts theposition of the warm end throttling device 78 and in the other case isarranged to switch one or more compressors on and off, according to thetemperature level required in the cold room.

To defrost the circulation space 65, a branch pipe 85 is led from thewarm end outlet into the said circulation space and in this branch pipe85 is arranged a valve 86 which can be opened to admit warm air to thecirculation space, the variable orifice operated by a lever 87 beingclosed during the defrosting process.

What is claimed is:

1. Air-heating and cooling apparatus, comprising:

a volute chamber having an inlet which opens tangentially into acircumferential region thereof, a warm air outlet inone end wall thereofand a cold air outlet in its other end wall of substantially smallerflow area than the warm air outlet, both of said outlets being incommunication with a central region of said volute chamber; means forsupplying compressed air to the circumferential region of the volutechamber through the inlet thereof; and a ring of guide vanes arrangedwithin the volute chamber in an annular zone between the circumferentialand central regions thereof,

the individual guide vanes of said guide vane ring being inclined so asto reflect air from the circumferential region into the central zone.

2. Apparatus as claimed in claim 1, wherein said volute chamber includestwo inlets which open tangentially into the circumferential regionthereof on opposite sides respectively of its circumference, whereinsaid means for supplying compressed air includes two air compressorsconnected respectively to said two inlets.

3. Apparatus as claimed in claim 1, including a heat exchangerpositioned between said compressed air supplying means and the inlet ofsaid volute chamber for removing the heat of compression from thecompressed air.

4. Apparatus as claimed in claim 1, wherein said in-- dividual guidevanes of the guide vane ring are inclined so that the air passingbetween them is given a tangential component of motion relative to theinside circumference of said guide vane ring.

5. Apparatus as claimed in claim 1, wherein the angle between each saidindividual guide vane and a correspond ing tangent to the circumferenceof the guide vane ring is less than 20.

6. Apparatus as claimed in claim 1, wherein a common control member isconnected to all the guide vanes of the guide vane ring and theindividual guide vanes are pivot ally adjustable about their inner edgesby means of. the said'common control member to vary the angle betweenthem and corersponding tangents to the inside circumference of the guidevane ring.

7. Air-heating and cooling a volute chamber having an inlet which openstangentially into a circumferential region thereof,

a warm air outlet in one end wall thereof and a cold air outlet in itsother end wall of substantially smaller flow area than said warm airoutlet,

both of said outlets being in communication with a central region ofsaid volute chamber;

means for supplying compressed air to the circumferential region of thesaid volute chamber through the inlet thereof,

a ring of guide vanes arranged within said volute chamber in an annularzone between the circumferential and central regions thereof;

the individual guide vanes of said guide vane ring being inclined so asto deflect air from the circumferential region into the central zone,and a warm air outlet pipe communicating with said Warm air outlet andhaving a length 25 to 30 times greater than the inner diameter of saidguide vane ring.

apparatus, comprising:

3. Apparatus as claimed in claim 7, wherein the bore of the warm airoutlet pipe at its inlet end is of the same diameter as the warm airoutlet opening and the walls of the said bore taper outwardly in thedirection towards its outlet end at an included angle of 5 to 8.

9. Apparatus as claimed in claim 7, wherein said warm air outlet pipe issurrounded by a water-cooling jacket with a helical partition positionedin the space between said outlet pipe and said jacket forming a helicalpassage for the flow of cooling water from one end of the said pipe tothe other.

16. Apparatus as claimed in claim 7, including an adjustable throttlingdevice positioned at the outlet end of said warm air outlet pipe.

11. Apparatus as claimed in claim 7, wherein means are also provided forswitching in one or more additional compressors to discharge into thecircumferential region of the volute chamber.

12. A refrigerating apparatus, comprising:

a volute chamber having an inlet which opens tangentiallyv into acircumferential region thereof,

a warm air outlet in one end wall thereof and a cold air outlet in itsother end wall of substantially smaller flow area than said warm airoutlet,

both of said outlets being in communication with a central region ofsaid volute chamber;

means for supplying-compressed air to the circumferential region of saidvolute chamber through the inlet thereof;

a ring of guide vanes arranged within the volute chamber in an annularzone between the circumferential and central regions thereof,

the individual guide vanes of said guide vane ring being inclined so asto deflect air from the circumferential region into the central zone;

a'cold chamber having heat-insulated main walls;

' an inner metal lining located within said cold chamber and in spacedrelation with respect to the main walls ,thereof; and

dividing plates arranged between the main walls and the metal liningproviding a cold air channel extending in adjoining convolutions aroundthe metal lining from the bottom to the top of said cold chamber,

munication with the lower end of said cold air channel and the upper endof said cold air channel being open to the atmosphere. 13. Apparatus asclaimed in claim 12, comprising in addition defrosting means operativewhen actuated, to shut off said cold air outlet from and connect thewarm air outlet to the lower end of said cold air channel.

References Cited by the Examiner UNITED STATES PATENTS 2,522,787 9/50Hughes 62--5 2,581,168 1/52 Bramley 62-5 2,731,511 1/56 Levitt 62-52,893,214 7/59 Hendal 625 FOREIGN PATENTS 759,440 10/56 Great Britain.

WILLIAM J. WYE, Primary Examiner.

the cold air outlet of the volute chamber being in com-'

1. AIR-HEATING AND COOLING APPARATUS, COMPRISING: A VOLUTE CHAMBERHAVING AN INLET WHICH OPENS TANGENTIALLY INTO A CIRCUMFERENTIAL REGIONTHEREOF, A WARM AIR OUTLET IN ONE END WALL THEREOF AND A COLD AIR OUTLETIN ITS OTHER END WALL OF SUBSTANTIALLY SMALLER FLOW AREA THAN THE WARMAIR OUTLET, BOTH OF SAID OUTLETS BEING IN COMMUNICATION WITH A CENTRALREGION OF SAID VOLUTE CHAMBER; MEANS FOR SUPPLYING COMPRESSED AIR TO THECIRCUMFERENTIAL REGION OF THE VOLUTE CHAMBER THROUGH THE INLET THEREOF;AND A RING OF GUIDE VANES ARRANGED WITHIN THE VOLUTE CHAMBER IN ANANNULAR ZONE BETWEEN THE CIRCUMFERENTIAL AND CENTRAL REGIONS THEREOF,THE INDIVIDUAL GUIDE VANES OF SAID GUIDE VANES RING BEING INCLINED SO ASTO REFLECT AIR FROM THE CIRCUMFERENTIAL REGION INTO THE CENTRAL ZONE